The US Secret Service, the law enforcement agency in charge of protecting the president, destroyed texts exchanged by officers during the January 6 Capitol attack, according to a government watchdog in a letter published Thursday.

The inspector general of the Department of Homeland Security, Joseph Cuffari, told Congress in a letter dated Wednesday that his office has had difficulty acquiring information from the Secret Service for the dates January 5 and 6, 2021.

The messages could be crucial in investigations by the House of Representatives and the Justice Department into whether Donald Trump and his close advisers encouraged the deadly insurgency by the former President's supporters at the US Capitol, which aimed to prevent Democratic rival Joe Biden from being certified as the winner of the November 2020 election.

During the day of the revolt, Secret Service agents were with Trump, as well as Vice President Mike Pence, who went into hiding at the Capitol when pro-Trump rioters shouted for his execution.

Read next: More evidence piles up against Trump in Jan 6 hearings

On June 29, a former White House worker testified to the House January 6 probe that Trump tried to force the Secret Service to send him to the Capitol to join his supporters that day.

"The Department notified us that many US Secret Service (USSS) text messages, from January 5 and 6, 2021, were erased as part of a device replacement program," Cuffari wrote in the letter first reported by The Intercept and later published by Politico.

"The USSS erased those text messages after OIG requested records of electronic communications" for a review of January 6, he said, referring to the Office of the Inspector General. Furthermore, he said that the agency had paused in providing other records to the OIG.

Tea was spilled in the last #Capitol riot hearing, as Cassidy Hutchinson revealed firsthand stories about #Trump's chaotic behavior before, during, and after the riots.#CapitolRiot #CapitolAttack #January6thHearings pic.twitter.com/7ko35ToJRM

— Al Mayadeen English (@MayadeenEnglish) June 29, 2022

Secret Service spokesperson Anthony Guglielmi denied the inspector general's claim in a statement. He stated that the agents' phones were being deleted as part of a planned replacement program that began six weeks before the OIG sought the information.

"The Secret Service notified DHS OIG of the loss of certain phones’ data, but confirmed to OIG that none of the texts it was seeking had been lost in the migration," he said. Cuffari's letter was sent to the chairmen of the Senate and House Homeland Security Committees.

Read next: Trump 'hardly knows' who his key former aide is after testimony

Representative Bennie Thompson, who also chairs the House committee examining the events of January 6, is the head of the House Homeland Security Committee. Their study reveals that Trump purposefully incited the insurgency as an attempted "coup".

The Secret Service has been chastised for failing to appropriately anticipate the prospect of armed Trump supporters carrying out a violent protest on January 6. Trump had appointed Tony Ornato, a top Secret Service official, as his deputy chief of staff at the time.

Ornato has rejected the testimony presented to the committee on January 6 by former Trump staffer Cassidy Hutchinson that Trump sought to push the Secret Service to transport him to the Capitol as his fans gathered. Other former White House officials, though, have backed Hutchinson's version.